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11 <br />• Pb, Mn and As. These metals will typically be included in <br />other sulfides such as chalcopyrite (Cu, Fe)S2, galena PbS, <br />sphalerite ZnS, arsenopyrite FeAsS, enargite Cu3AsS4 and <br />tennantite (Cu, Fe, Zn, Ag)12As4SI3. The information con- <br />cerning the dissolution of these minerals is not as complete <br />as that for pyrite, probably because they aren't common in <br />coal. Some information can be gained from hydrometallurgy <br />and solution mining studies (19, 20). Also, Wentz (8) has <br />a good summary of the possible weathering reactions for <br />these minerals. <br />In all these minerals, the anions of sulfur and arsenic <br />will be oxidized by oxygen. The key to the dissolution is <br />whether the anion is a complex sulfo salt, such as FeS2, <br />• FeAsS, (Fe, CU) S2, or CU3AsS4, or a simple sulfide such <br />as FeS, Ag2S, PbS or ZnS. In the former case, the dissolu- <br />tion makes the water acidic; for example: <br />2FeAsS(s) + 13/202 + 3H2O + 2Fe2+ + 2SO4 + 2H2As04 + 2H+ (16) <br />In the case of simple sulfides, no hydrogen ions are released <br />upon dissolution; for example: <br />PbS(s) + 202 +_" Pb2+ + S04 (17) <br />So complex sulfo minerals weather to produce acidic waters <br />but simple sulfides do not produce acidic drainage. <br />Once the pH of the water has become low enough, con- <br />gruent dissolution reactions of the simple sulfides are also <br />possible. <br />• PbS(s) +-H+(afl) f Pb2+(aa) + HS (aa) (18) <br />HS + 202 S04 + H+ (19)